This invention relates to a process for the production of polyesters from isophthalic acid or terephthalic acid. In particular, this invention relates to a process for the production of unsaturated polyesters from isophthalic acid or terephthalic acid, a polyol and an unsaturated aliphatic polycarboxylic acid.
When isophthalic acid and terephthalic acid were substituted for phthalic anhydride in the production of polyesters, the one-stage process used with phthalic anhydride was not as effective. The art developed a two-stage process in which polyesters were produced from isophthalic acid or terephthalic acid, a polyhydric alcohol, or polyol, and a saturated or unsaturated polycarboxylic acid.
One two-stage process is disclosed in U.S. Pat. No. 2,904,533 (Carlson et al). In the first stage the isophthalic acid is polycondensed with all of the glycol until essentially a zero acid number product mixture is obtained. Then, this product mixture has an unsaturated acid, such as maleic acid or anhydride, added to it until the desired acid number and unsaturated polyester is obtained. This two-stage process was subsequently improved by conducting the first stage reaction so most but not all of the water of esterification that theoretically could be produced was removed from the first stage. Another improvement on this two-stage process is the use of two dihydric alcohols of different carbon atom content. This process is disclosed in U.S. Pat. No. 3,196,131 (Mayer et al.). The higher boiling alcohol is charged to the first stage along with the aromatic dicarboxylic acid such as isophthalic acid. The unsaturated acid, the other dihydric alcohol and remaining first alcohol, if any, are charged to the second stage.
Another two-stage process is disclosed in U.S. Pat. No. 3,345,339 (Parker et al.). In the first stage a part of the polyol ingredient is reacted with isophthalic acid or terephthalic acid in the presence of an esterification catalyst, a tin compound, and in the substantial absence of an alpha, beta-ethylenically unsaturated polycarboxylic acid. In the second stage an alpha, beta-ethylenically unsaturated polycarboxylic acid is reacted with the reaction product mixture of the first stage.
All of these two-stage processes endeavor to increase the effectiveness of using isophthalic acid or terephthalic acid from that of a one-step process. In the two-stage process there is a serious disability over the one-stage process. The two-stage process takes from two to three times the number of hours to complete a polyester preparation as does the one-stage process. The above discussed patents purport to overcome this disadvantage in duration of processing time. The reduction in the duration of processing time effected by the two-stage process used in the prior art can be improved.
The object of this invention is to provide a process that reduces the processing time in the production of a polyester in a two-stage process from isophthalic acid or terephthalic acid, a polyol and a saturated or unsaturated aliphatic polycarboxylic acid.